Multi-shell emulsion particle

ABSTRACT

A multi-shell emulsion particle of dry state structure having one or more of penetrating pore(s) connecting the surface layer of the particle with the interior of the particle and having a particle diameter of from 0.1 to 5.0μ preferably from 0.1 to 1.2μ. The particles can be prepared by carrying out emulsion polymerization of a vinyl monomer (a) containing from 5 to 80% by weight of an unsaturated carboxylic acid to obtain a polymer (A), forming a polymer (B) in the presence of a particle consisting of the resultant polymer (A) while adding a vinyl monomer (b) in an amount of 10 times by weight or less and at a rate of 3 times by weight per hour or more for the weight of the polymer (A), and treating the resultant multi-shell emulsion polymer with an alkaline material to neutralize and swell the polymer (A); or, after the neutralization treatment, further forming a polymer (C) by adding and emulsion-polymerizing a vinyl monomer (c) in an amount of 20 times by weight or less for the total weight of the polymer (A) and polymer (B). The emulsion particle is useful as a component of resin compositions for paints, paper-coating and heat-sensitive recording materials.

This application is a divisional of application Ser. No. 08/189,995,filed Feb. 1, 1994, now U.S. Pat. No. 5,409,776 which is a continuationof application Ser. No. 07/730,236, filed Jul. 15, 1991 now abandoned.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to a multi-shell emulsion particle whichis useful as an additive to coating compositions for paints, papercoating and information recording papers, and has a penetrating pore inthe interior of the particle.

b) Description of the Related Art

In recent years, high molecular weight polymer particles prepared byemulsion polymerization have been studied for utilization as organicpigments in various fields.

The most commonly used polymer particles are homogeneous and solid,emulsion-polymerized polystyrene particles having a diameter of 0.2 to0.5μ. For example, Japanese Laid-Open Patent 59741 (1984) discloses aprocess for copolymerizing an unsaturated carboxylic acid and a vinylmonomer in the presence of an anionic surface active agent and/or anonionic surface active agent to prepare a copolymer emulsion whereinmore than 90% of the particles have a diameter of 0.20 to 0.28μ.

The patent also describes that the copolymer emulsion can be used as anorganic pigment in applications such as paper coating and paints.However, the organic pigment obtained by the process fails to providesufficient hiding power, brightness and gloss, and no practicaladvantage is obtained unless it is used in a large amount. Consequently,the pigment leads to problems such as high cost and weight increase.

In order to further improve hiding power, brightness and gloss,conversion from the above homogeneous and solid particles to poredemulsion particles has recently been proposed in U.S. Pat. No.4,427,836. The pored emulsion particles are obtained by mixing a corematerial, a polymer dispersion, formed by copolymerizing at least 5% byweight of an unsaturated carboxylic acid, with at least one of amonoethylenically unsaturated shell monomer for forming a shell polymer,carrying out emulsion polymerization, neutralizing the resultingemulsion with an aqueous, volatile base to swell the core polymer andthereafter drying to form minute openings in the interior of theparticles. When the emulsion particles thus obtained are used for anorganic pigment, the hiding power and brightness have been found to bebetter, though not satisfactory, than those of the above homogeneous andsolid particles.

The swelled core polymer in the interior of the particles containmoisture. The moisture evaporates by drying the particles to make thevoid. However, the moisture must transmit through the layer of shellpolymer of particles and hence evaporation becomes difficult. Largervoids lead to larger amount of moisture contained and result in adisadvantage of decreased drying ability. When the above particles areused as an organic pigment for paper coating, remarkable improvementcannot be observed on printability such as receptivity to inks,ink-setting ability and blistering property.

On the other hand, Japanese Laid-Open patent 281886 (1988) discloses anexample for improving coloring sensitivity of a heat-sensitive recordingpaper by employing the above particles having minute openings for theundercoat of the paper to enhance heat insulation property. Theheat-sensitive recording paper prepared by the process has someimprovement in color developing sensitivity as compared with recordingpapers prepared by using inorganic pigments or urea resin. However, noimprovement is observed on the foreign matter adhesion to a thermal headand sticking.

As mentioned above, emulsion particles having minute openings in theinterior have been improved in view of hiding power and brightness as anorganic pigment. On the other hand, lack of oil absorbing property andgas permeability due to the particle structure is a serious disadvantageas a pigment and leads to problems in practical use.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide an excellentmulti-shell structured emulsion particle without impairing hiding powerand brightness of an organic pigment.

Another object of the present invention is to provide a multi-shellstructured emulsion particle which can be applied to an organic pigmentwhich is useful for paint, paper coating and heat-sensitive recordingmaterials.

The above objects of the present invention can be accomplished byproviding a multi-shell emulsion particle comprising a dry statestructure having one or more of penetrating pore connecting the surfacelayer of the particle with the interior thereof and a particle diameterof from 0.1 to 5.0μ.

A preferred multi-shell emulsion particle has a void in the interior ofthe particle in a dry state and a pore penetrating from the particlesurface to the interior void. The particle diameter is preferably in therange of from 0.1 to 1.2μ.

The above emulsion particle can be prepared by carrying out emulsionpolymerization of a vinyl monomer (a) comprising from 5 to 80% by weightof an unsaturated carboxylic acid, forming a polymer (B) in the presenceof a particle consisting of the resultant polymer (A) while adding avinyl monomer (b) in an amount of 10 times by weight or less and at arate of 3 times by weight per hour or more for the weight of the polymer(A), and treating the resultant multi-shell emulsion polymer with analkaline material to neutralize and swell the polymer (A); or, after theneutralization treatment, further forming a polymer (C) by adding andemulsion-polymerizing a vinyl monomer (c) in an amount of 20 times byweight or less for the total weight of the polymer (A) and polymer (B).

The morphological characteristics of the multi-shell emulsion particlein the invention lead to an excellent oil absorption property and gaspermeability which have been lacking in conventional organic pigments.The morphological and functional features of the particle do not giveadverse effect on the hiding power and brightness.

For example, in cases where the particle is used for a pigment or afiller of coating compounds and paper coating compositions, the emulsionparticle can replace a portion or the whole of titanium dioxide, kaolinclay and calcium carbonate. In these cases, auxiliary functions such asoil absorption property and gas permeability can be provided withoutimpairing the excellent hiding power and brightness. The emulsionparticle is also useful for heat-sensitive recording materials. Further,the emulsion particle has effect on weight saving and improves hardness,abrasion resistance and thermal resistance. Hence the emulsion particlecan also be applied as an additive to various compositions which areused for paper, metals, plastics, fibers and cloth.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a scanning type electron microscope photograph (magnification20000) of a multi-shell emulsion particle obtained by the process ofPolymerization Example 1 and having a penetrating pore.

DETAILED DESCRIPTION OF THE INVENTION

The multi-shell emulsion particle of the invention will be illustratedon the monomer composition of polymer constituting each layer of theparticle.

The polymer (A) is prepared by emulsion polymerization of the vinylmonomer (a) which contains the unsaturated carboxylic acid. The vinylmonomer (a) is a compound or a combination of compounds selected frommethyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate andother (meth)acrylate esters; styrene, α-methylstyrene, vinyltoluene andother aromatic vinyl compounds; (meth)acrylonitrile and other vinylcyano compounds; vinyl chloride, vinylidene chloride and otherhalogenated vinyl compounds; and butadiene. The unsaturated carboxylicacid is a compound or a mixture of compounds selected from (meth)acrylicacid, crotonic acid, fumaric acid, itaconic acid and other monobasic ordibasic acids; maleic acid alkyl ester, fumaric acid alkyl ester andother monoalkyl esters of dibasic acids. Acrylic acid and methacrylicacid are preferred in particular. The amount of the unsaturatedcarboxylic acid copolymerized in preferably from 5 to 80 parts byweight, more preferably from 10 to 50 parts by weight for 100 parts byweight of the vinyl monomer (a). When the amount of the unsaturatedcarboxylic acid in the polymer (A) is less than 5 parts by weight,treatment with the alkaline material cannot sufficiently swell thepolymer (A) and cannot form the penetrating pore. On the other hand, theamount of 80 parts by weight or more impairs stability inpolymerization, develops a large amount of coagulated products andcannot form a stable emulsion.

In the process of preparing the polymer (A), a functional monomer isused, if desired, in order to stabilize the emulsion of the polymer (A).Exemplary functional monomers which can be used include unsaturatedsulfonic acid salts such as sodium styrenesulfonate; unsaturated basessuch as dimethylaminoethyl methacrylate; (meth)acrylate esters such as2-hydroxyethyl (meth)acrylate and glycidyl (meth)acrylate; and amidessuch as (meth)acrylamide and N-methylol(meth)acrylamide.

A crosslinkable monomer can also be used as a component of the polymer(A) so long as the monomer can copolymerize with the monomer forconstituting the polymer (A). Examples of the crosslinkable monomerinclude divinylbenzene, ethylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate and other monomers having at leasttwo polymerizable unsaturated bonds in a molecule. The amount of thecrosslinkable monomer is in the range of usually from 0 to 8% by weight,preferably from 0.1 to 5% by weight, more preferably from 0.2 to 1% byweight for the weight of the monomer constituting the polymer (A).

Application of the crosslinkable monomer increases molecular weight ofthe polymer (A) and inhibits diffusion of theexterior-layer-constituting polymer (B) into the interior of theparticle. Thus the polymer (B) can be favorably formed in the exteriorof the particle. Also it can be favorably carried out in the treatmentwith the alkaline material to inhibit dissolution of the polymer (A) inthe aqueous phase and accompanied viscosity increase of the aqueousphase. However, the amount of the crosslinkable monomer exceeding 8% byweight inhibits swelling of the polymer (A) by the alkaline material andthus particles of the desired shape cannot be obtained.

In the next step, the vinyl monomer (B) is added to the particlesconsisting of the polymer (A) and emulsion polymerization is carried outto form the polymer (B) in the exterior of the particles of polymer (A).

The vinyl monomer (b) which can be used includes, for example, acompound or a combination of the compound selected from styrene,α-methylstyrene, vinyltoluene and other aromatic vinyl compounds; methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate and other(meth)acrylate esters; (meth)acrylonitrile and other vinyl cyanocompounds; vinyl chloride, vinylidene chloride and other halogenatedvinyl compounds; and butadiene.

A functional monomer may be used, if desired, in order to providestability of emulsion in the preparation process. Exemplary functionalmonomers which can be used include (meth)acrylic acid, crotonic acid,itaconic acid, and other unsaturated carboxylic acids; sodiumstyrenesulfonic acid and other unsaturated sulfonic acid salts;2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate and other(meth)acrylate esters; and (meth)acrylamide andN-methylol(meth)acrylamide.

As mentioned above, the vinyl monomer (b) can contain the unsaturatedcarboxylic acid in order to provide stability for the emulsion. Theproportion of the unsaturated carboxylic acid in the vinyl monomer (b)is usually lower than the proportion in the vinyl monomer (a) andpreferably in the range of from 0.1 to 2.0% by weight. When theproportion of the unsaturated carboxylic acid is higher in the vinylmonomer (b) than in the vinyl monomer (a), swelling ability of thepolymer (B) becomes larger than that of the polymer (A) and the desiredparticle having a penetrating pore cannot be obtained.

The vinyl monomer (b) can also contain a crosslinkable monomer which cancopolymerize with the vinyl monomer (b) in order to improve theresistance of the desired particle to blocking, heat and solvent. Thecrosslinkable monomers which can be used include, for example, divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropanetrimethacrylate and other monomers having two or more polymerizableunsaturated bonds in a molecule. The effect of the crosslinkable monomercan be exhibited in the range of usually from 0 to 3% by weight,preferably from 0.1 to 3% by weight, more preferably from 0.2 to 2% byweight for the weight of the above vinyl monomer (b). Use of more than3% of weight is unfavorable because stability in the polymerization isliable to be impaired.

No particular restriction is imposed on the combination of the abovemonomers. However, it is preferred to select the monomers so that thepolymer (B) has a glass transition temperature of 50° C. or above,preferably 70° C. or above.

The above multi-shell emulsion particle is prepared by common emulsionpolymerization process. In the process of the invention, the polymer (B)is formed in the exterior of a core particle consisting of the polymer(A) and then, after or during the treatment with the below describedalkaline material, the vinyl monomer (c) is added and emulsionpolymerized to form the polymer (C) in the exterior of a particle of thepolymer (B).

The vinyl monomer (c) which can be used for forming the polymer (C)includes, for example, styrene, -methylstyrene, vinyltoluene and otheraromatic vinyl compounds; methyl (meth)acrylate, ethyl (meth)acrylate,butyl (meth)acrylate and other (meth)acrylate esters;(meth)acrylonitrile and other vinyl cyano compounds; vinyl chloride,vinylidene chloride and other halogenated vinyl compounds; andbutadiene. These monomers can be used singly or in combination.

In the addition and emulsion polymerization of the vinyl monomer (c), afunctional monomer can be used, if desired, in order to providestability of the emulsion. Exemplary functional monomers which can beused include (meth)acrylic acid, crotonic acid, itaconic acid and otherunsaturated carboxylic acids; sodium styrenesulfonate and otherunsaturated carboxylic acid salts; 2-hydroxyethyl (meth)acrylate,glycidyl (meth)acrylate and other (meth)acrylate esters; and(meth)acrylamide and N-methylol (meth)acrylamide. The amount of thefunctional monomer is in the range of usually from 0 to 20% by weight,preferably from 0.1 to 10% by weight, more preferably from 0.1 to 5% byweight for the weight of the above vinyl monomer (c). When thefunctional monomers are used more than 20% by weight, secondaryparticles are liable to develop, moisture resistance decreases andviscosity increase in the alkali treatment becomes larger. Theseinfluences make practical use difficult. The preferred amount of theunsaturated carboxylic acid in the vinyl monomer (c) is 3% by weight orless. Use of more than 3% accelerates coagulation.

The vinyl monomer (c) can be incorporated with a crosslinkable monomer,if desired. The crosslinkable monomers which can be used include, forexample, divinylbenzene, ethylene glycol di(meth)acrylate,trimethylolpropane trimethacrylate and other monomers having at leasttwo polymerizable unsaturated bonds in a molecule. The amount of thecrosslinkable monomer is in the range of usually from 0 to 3% by weight,preferably from 0.1 to 3% by weight, more preferably from 0.2 to 2% byweight for the weight of the above vinyl monomer (c).

Use of the crosslinkable monomer can improve resistance to blocking,heat and solvent. However, use of more than 3% inhibits swelling of thepolymer (A) in the treatment with the alkaline material. On the otherhand, addition of less than 0.1% by weight, effect of the crosslinkablemonomer is poor.

No particular restriction is placed on the combination of the abovemonomers. However, the glass transition temperature of the polymer (C)obtained is preferably 50° C. or above, more preferably 70° C. or above.

The process for forming each layer of the multi-shell emulsion particlewill be illustrated below.

Formation of each layer is generally carried out by common emulsionpolymerization process in the presence of a surface active agent and apolymerization initiator.

The surface active agents which can be used include, for example, asingle agent or a combination of the agent selected from anionic surfaceactive agents such as sodium alkylbenzenesulfonate, sodium alkylsulfate,sodium dialkylsulfosuccinate and naphthalenesulfonic acid/formaldehydecondensate; and nonionic surface active agents such as polyoxyethylenealkyl ether, polyoxyethylene alkylphenol ether, ethylene oxide/propyleneoxide block copolymer and sorbitan fatty acid ester.

No particular limitation is imposed upon the amount of the surfaceactive agent. The amount is usually from 0.1 to 10% by weight for thetotal weight of the monomer used in each layer.

Any kind of polymerization initiator which is commonly used in emulsionpolymerization processes can be used for the present invention.Representative polymerization initiators include, for example,persulfates such as potassium persulfate, sodium persulfate and ammoniumpersulfate; organic peroxides such as benzoyl hydroperoxide; and azocompounds such as azobisisobutyronitrile. The polymerization initiatorcan be used, if desired, together with a reducing agent in the form of aredox type initiator.

In the preparation of an emulsion consisting of the polymer (A),polymerization is carried out by adding the monomer (a) at one time, inportions or continuously as a stream of droplets in the presence of theabove surface active agent and the polymerization initiator. Thepolymerization is carried out at a temperature of 20° to 90° C. in anitrogen atmosphere.

In emulsion polymerization, a process for adding a vinyl monomer in thepresence of a seed particle in order to provide a polymerization spot ofa particle has been known as "seed polymerization". The process can alsobe used in the invention.

No particular restriction is imposed upon the composition of the seedparticle. However, the diameter of the seed particle is preferably 0.07μor less in order to give no adverse effect on the performance of theparticle finally obtained.

The diameter of the particle consisting of the polymer (A) thus formedis preferably from 0.08 to 0.2μ, more preferably from 0.1 to 0.15μ. Whenthe particle diameter is less than 0.08μ, the below-described polymer(B) is formed in the interior of the particle. On the other hand, whenthe particle diameter exceeds 0.2μ, the polymer (B) covers the particle.In both cases, the desired particle having a penetrating pore cannot beobtained.

Polymerization is further carried out by adding the vinyl monomer (b) atone time, in portions or continuously to the thus-formed emulsionconsisting of the polymer (A).

Alternatively, the emulsion consisting the polymer (A) may be previouslyprepared in a separate step, and charged to a new polymerization vessel.Successively vinyl monomer (b) may be added as above to carry outpolymerization. That is, the preparation processes of the polymer (A)and the polymer (B) may be carried out continuously in one step,individually in a separate step or in a combined step. No particularrestriction is placed on the polymerization step.

The amount of the vinyl monomer (b) is usually from 1 to 10 times byweight, preferably from 1.5 to 8 times by weight, more preferably from 2to 6 times by weight for the weight of the polymer (A). When the amountof monomer (b) is less than the same weight as the polymer (A), theparticle consisting of the polymer (A) is very imperfectly covered withthe polymer (B) and thus the desired particle having the penetratingpore cannot be obtained. On the other hand, when the amount of themonomer (b) exceeds 10 times by weight, the particle is completelycovered with the polymer (B) and hence the desired particle having thepenetrating pore cannot be obtained. The vinyl monomer (b) is added at arate of generally 3 times or more, preferably from 4 to 12 times, morepreferably from 4.5 to 10 times, most preferably from 5 to 9 times byweight per hour for the weight of the polymer (A). When the weight isless than 3 times, the charging rate is too slow and polymerization iscarried out in the neighborhood of the surface layer of the particlecomposed of the polymer (A). Thus the particle is completely coveredwith the polymer (B) and the desired particle having the penetratingpore cannot be obtained. On the other hand, when the amount is more than12 times, the charging rate is too quick and the polymer (B) forms inthe interior of the particle. Thus the desired particle having thepenetrating pore cannot be obtained.

The polymerization is carried out in the presence of the abovepersulfate at a temperature of preferably from 60° to 100° C., morepreferably from 70° to 90° C. Polymerization temperature exceeding 100°C. is disadvantageous because increased pressure is required.Polymerization temperature lower than 60° C. leads to decreasedconversion rate of the vinyl monomer (b) during polymerization and astable emulsion cannot be obtained.

By simultaneous use of persulfate and a suitable reducing agent, thepolymerization can be carried out with a high conversion ratio even at atemperature of from 30° to 50° C. However, the desired particle havingthe penetrating pore cannot be obtained. The phenomenon is assumed thatthe polymer (B) is formed in the vicinity of the surface layer of theparticle composed of the polymer (A).

The above-obtained emulsion particle is treated with the alkalinematerial to give the desired multi-shell emulsion particle which has avoid, a preferred morphology, in the interior and at least one porepenetrating from the particle surface to the interior void and has aparticle diameter in the range of from 0.1 to 5μ, preferably from 0.1 to1.2μ.

Further, the vinyl monomer (c) is added after the treatment with thealkaline material and the most exterior layer consisting of the polymer(C) is formed by polymerization to obtain another desired multi-shellemulsion particle which has a void in the interior and at least one porepenetrating from the particle surface to the interior void and has aparticle diameter in the range of from 0.1 to 5.0μ, most preferably from0.1 to 1.2μ without closing the penetrating pore, and increasing athickness of the exterior layer and a strength of the particle itself.In the object of the present invention, the most exterior layer is morepreferably polymerized.

The amount of the vinyl monomer (c) is preferably from 1 to 20 times,more preferably from 1.5 to 15 times, most preferably from 2 to 10 timesfor the total weight of polymer (A) and polymer (B). When the amount ofthe vinyl monomer (c) is more than 20 times for the total weight ofpolymer (A) and polymer (B), the polymer (C) completely covers thepolymer (B), the penetrating pore does not develop on the particlesurface and hence the desired particle cannot be obtained.

The emulsion particle obtained by forming the polymer (B) is treatedwith the alkaline material by the following process.

Exemplary alkaline materials which can be used include inorganicalkaline compounds such as potassium hydroxide and sodium hydroxide;volatile alkaline compounds such as ammonia; and organic alkalinecompounds such as dimethylethanolamine and trimethylamine.

The alkali treatment is carried out in the range of pH 7 to pH 12,preferably pH 8 to pH 11. In lower than pH 7, swelling becomes difficultand the desired particle cannot be obtained. On the other hand, inhigher than pH 12, stability of the emulsion is severely impaired andthe treatment itself cannot be smoothly carried out.

The alkali treatment is carried out at a temperature of from 50° to 100°C., preferably from 70° to 98° C., more preferably from 80° to 95° C.The temperature lower than 50° C. causes incomplete plasticization ofthe exterior layer and hence leads to insufficient swelling of theparticle. As a result, the desired particle cannot be obtained.

The thus-obtained multi-shell emulsion particle having a particlediameter of from 0.1 to 5.0μ, most preferable 0.1 to 1.2μ ischaracterized by having a void in the interior of the particle and atleast one penetrating pore which connects particle surface with theinterior of the particle.

The mechanism for developing the morphology of the multi-shell emulsionparticle in the invention is not clear. When the vinyl monomer (b) ispolymerized under the above mentioned conditions, it is assumed that thepolymer (A) is not completely covered with the polymer (B) and partlyexposed to the surface of the particle. As a result, in the alkalitreatment of the particle, the polymer (A) swells and forms thepenetrating pore to the interior of the particle. At the same time, thevinyl polymer (C) polymerizes on the surface of the polymer (B). Thepolymer (C) is thought to be formed while remaining the pore as intactto obtain the particle having the desired structure. The structure ofsaid particle can be identified with ease by observing the particleitself or a section of the particle with an electron microscope.

The diameter of the emulsion particle obtained in the invention isusually from 0.1 to 5.0μ, preferably from 0.1 to 4.0μ, most preferablyfrom 0.1 to 1.2μ, further preferably from 0.3 to 1.0μ. When the particlediameter is less than 0.1μ, the particle cannot be used for an organicpigment because of considerably low hiding power and brightness, eventhough the particle has the above interior structure. On the other hand,the particle having a diameter exceeding 5μ, more exactly 1.2μ cannotform a stable emulsion.

The particle of the invention has hiding power and brightness which areequivalent or superior to those of the emulsion particle having a singlyhollowed structure and additionally has an excellent oil absorptionproperty and gas permeability.

The reason is not clear and assumed that the void ratio in the interiorof the particle is extremely enhanced due to the presence of usuallyfrom one to several penetrating pores and, at the same time, theexistence of the penetrating pore provides the excellent oil absorptionproperty and gas permeability for the particle.

As a result of the above characteristics, the multi-shell emulsionparticle of the invention can increase hiding power and brightness andadditionally enhance oil absorption property and gas permeability incases where the particle is used for coating compounds, paper coatingcompositions or heat-sensitive recording materials. The particle canreplace a portion or the whole of pigments such as titanium dioxide,clay and kaolin which are commonly added to the above compounds,compositions and materials, and can also provide specific functions suchas oil absorption property and gas permeability.

EXAMPLE

The present invention will hereinafter be illustrated in detail by wayof examples. Parts and percent indicate parts by weight and percent byweight, respectively.

[Preparation of multi-shell emulsion particle]

Polymerization Example 1

To a separable flask equipped with a stirrer, thermometer and a refluxcondenser, 2500 parts of water were charged and heated to 80° C. withstirring while replacing the atmosphere with nitrogen. The internaltemperature was maintained at 80° C., 1.5 parts of potassium persulfatewas added as a polymerization initiator and dissolved.

An emulsion was previously prepared by adding 16 parts of styrene, 0.3part of methacrylic acid and 0.2 part of divinylbenzene with stirring toa solution containing 0.2 part of sodium dodecylsulfate in 7 parts ofwater.

The emulsion thus prepared was charged to the separable flask andreacted for an hour to prepare a seed particle emulsion.

At this stage, a small amount of the seed particle emulsion was sampledand the diameter of the emulsion particle was measured by a dynamiclight scattering method. The diameter was 0.06μ.

Separately, an emulsion of the vinyl monomer (a) was prepared by adding55 parts of methyl methacrylate, 5 parts of butyl acrylate and 40 partsof methacrylic acid with stirring to a solution containing 0.3 part ofsodium dodecylsulfate in 40 parts of water.

To the seed particle emulsion, the emulsion thus obtained wascontinuously added over an hour and reacted. After finishing theaddition, the reaction mixture was aged for an hour to obtain thepolymer (A). The diameter of the particle consisting of the polymer (A)was 0.12μ by a dynamic light scattering analysis.

Successively, a solution containing 3 parts of ammonium persulfate in 30parts of water is added as a polymerization initiator. Separately anemulsion of the vinyl monomer (b) was prepared by adding 468 parts ofmethyl methacrylate, 120 parts of butyl acrylate and 12 parts ofmethacrylic acid with stirring to a solution of 1.2 parts of sodiumdodecyl sulfate in 240 parts of water. The emulsion of monomer (b) thusobtained was continuously added over an hour to the above emulsion ofthe polymer (A) and reacted. After finishing the addition, the reactionmixture was further aged for 2 hours to form the polymer (B) on thesurface of the polymer (A).

After finishing the polymerization, 490 parts of the emulsion thusobtained and 78 parts of water were charged to another separable flaskequipped with a stirrer, thermometer and a reflux condenser and 8.5parts of a 28% aqueous ammonia solution were added with stirring. Theemulsion was pH 10.0 after addition of ammonia. Then the internaltemperature of the flask was increased to 85° C. and stirring wascontinued for 30 minutes at the same temperature to carry out treatmentwith the alkaline material.

Successively, a solution containing 0.5 part of ammonium persulfate in 5parts of water was added as a polymerization initiator. Separately anemulsion of the vinyl monomer (c) was prepared by adding 297 parts ofstyrene and 3 parts of acrylonitrile with stirring to a solutioncontaining 0.6 part of sodium dodecylsulfate in 120 parts of water. Theemulsion of monomer (c) thus obtained was continuously added over 90minutes to the emulsion of the polymer (C) and reacted. After finishingthe addition the reaction mixture was further aged for 90 minutes toform the polymer (C) on the surface of the polymer (B).

The emulsion thus obtained had a non-volatile content of about 40%. Theparticle had a penetrating pore and a diameter of 0.50μ.

Polymerization Examples 2-5

The same procedures as described in Polymerization Example 1 was carriedout by adding the same amount of the vinyl monomer (a) and changing itscomposition alone. The results are illustrated in Table 1.

Comparative Polymerization Examples 1-2

In Polymerization Example 1, the seed particle emulsion was prepared bychanging the amount of sodium dodecylsulfate from 0.2 part to 2 parts.As a result, the particle of the polymer (A) had a diameter of 0.06μ bya dynamic light scattering analysis. Thereafter the same procedures asdescribed in Polymerization Example 1 were carried out. Results areillustrated in Table 1 as Comparative Polymerization Example 1.

Further, similarly to Comparative Polymerization Example 1, the amountof sodium dodecylsulfate was changed from 0.2 part to 0.02 part. As aresult, the polymer (A) had a diameter of 0.26μ by a dynamic lightscattering analysis. The results are illustrated in Table 1 asComparative Polymerization Example 2.

Comparative Polymerization Example 3

In Polymerization Example 1, 1 part of methacrylic acid was used in thevinyl monomer (a) and the same procedures as described in PolymerizationExample 1 were carried out. The results are illustrated in Table 1 asComparative Polymerization Example 3.

Comparative Polymerization Example 4-5

Procedures of Polymerization Example 1 were repeated except that 85parts of methacrylic acid were used in the vinyl monomer (a). Resultsare illustrated in Table 1 as Comparative Polymerization Example 4.

Procedures of Polymerization Example 1 were repeated except that 10% byweight of a crosslinkable monomer divinylbenzene was used for the weightof the vinyl monomer (a). Results are illustrated in Table 1 asComparative Polymerization Example 5.

Polymerization Examples 6-12

Procedures of Polymerization Example 1 were repeated except that thesame amount of the vinyl monomer (b) was added and only the compositionwas varied. Results are illustrated in Table 2 as PolymerizationExamples 6-10.

Procedures of Polymerization Example 1 were repeated except that theaddition amount of the vinyl monomer (b) was changed. The results areillustrated in Table 2 as Polymerization Examples 11-12.

Comparative Polymerization Example 6

In Polymerization Example 1, the emulsion was prepared by changing theprocedures for forming the polymer (B) as follows.

The polymer (A) was prepared by repeating the procedures described inPolymerization Example 1. Thereafter the reaction mixture was cooled to30° C., 3 parts of sodium hydrogen sulfite were added, followed byadding a solution containing 3 parts of ammonium persulfate in 30 partsof water and thereafter continuously adding an emulsion containing thesame vinyl monomer (b) as in Polymerization Example 1 over an hour whilemaintaining the reaction temperature at 30° C. After finishing theaddition, the reaction mixture was warmed to 80° C. and aged for 2hours. Thus the polymer (B) was formed by redox polymerization on thesurface of the polymer (A). Thereafter the same procedures were carriedout as described in Polymerization Example 1. Results are illustrated inTable 2.

Comparative Polymerization Examples 7-8

Procedures of Polymerization Example 1 were repeated except that thevinyl monomer (b) containing 20% of methacrylic acid was used. Resultsare illustrated in Table 2 as Comparative Polymerization Example 7.

Procedures of Polymerization Example 1 were repeated except that 5% ofdivinylbenzene was used for the weight of the vinyl monomer (b). Resultsare illustrated in Table 2 as Comparative Polymerization Example 8.

Comparative Polymerization Examples 9-12

The same procedures described in Polymerization Example 1 were carriedout except that the emulsion containing the vinyl monomer (b) wascontinuously added over 6 hours and reacted. Results are illustrated inTable 2 as Comparative Polymerization Example 9.

In Comparative Polymerization Example 10, the emulsion of the vinylmonomer (b) was added over 20 minutes.

In Comparative Polymerization Examples 11 and 12, the addition amount ofthe vinyl monomer (b) was varied. Results are illustrated in Table 2.

Examples 13-19

In Polymerization Examples 13-16, the procedures described inPolymerization Example 1 were carried out by adding the same amount ofthe vinyl monomer (c) and by changing the composition of the vinylmonomer (c) alone.

In Polymerization Examples 17-18, the procedures described inPolymerization Example 1 were carried out by changing the additionamount of the vinyl monomer (c).

In Polymerization Example 19, the procedures of Polymerization Example 1were repeated except that the addition of the vinyl monomer (c) wasomitted and only the treatment with the alkaline material was conducted.

Results are illustrated in Table 3.

Comparative Polymerization Examples 13-16

In Comparative Polymerization Example 13, procedures described inPolymerization Example 1 were carried out by using the vinyl monomer (c)containing 5% of methacrylic acid.

In Comparative Polymerization Example 14, 5% of divinylbenzene was usedin the procedures of Polymerization Example 1.

In Comparative Polymerization Example 15, procedures described inPolymerization Example 1 were repeated except that treatment with thealkaline material and polymerization of the vinyl monomer (c) wereconducted at pH 6.5.

In Comparative Polymerization Example 16, the procedures ofPolymerization Example 1 were repeated except that the addition amountof the vinyl monomer (c) was varied.

Results are illustrated in Table 3.

Oil absorption was measured on the particles prepared above according toJIS K-5101. Sample powder was prepared by drying the emulsion at 50° C.for 24 hours, crushing in a mortar and passing through a #150 meshsieve. Results are illustrated in Tables 1-3.

                                      TABLE 1                                     __________________________________________________________________________                                         Particle diameter                                                                      Particle   Oil                           Composition of vinyl monomer (a)                                                                          of polymer (A)                                                                         diameter                                                                           Penetrating                                                                         absorption                    MMA BA EA  AN  MAc HEMA DVB [μ]   [μ]                                                                             pore  [%]                  __________________________________________________________________________    Poly. Ex.                                                                     1        55  5          40           0.12     0.50 ◯                                                                       83                   2            20 30  10  40       0.2 0.10     0.56 ◯                                                                       82                   3        70     10      15  5        0.13     0.48 ◯                                                                       79                   4            40         60       0.5 0.09     0.57 ◯                                                                       81                   5        50  32     5   8   5    0.1 0.12     0.43 ◯                                                                       80                   Comp. Poly. Ex.                                                               * 1      55  5          40           0.06     0.18 X     53                   * 2      55  5          40           0.26     1.15 X     55                   3        94  5          1            0.11     0.43 X     54                   ** 4     10  5          85           --       --   --    --                   5        45  5          40       10  0.07     0.42 X     51                   __________________________________________________________________________     * Particle diameter of seed emulsion differs from Polymerization Example      1.                                                                            ** Coagulation occurs in polymerization process. Emulsion cannot be           obtained.                                                                

                                      TABLE 2                                     __________________________________________________________________________                                    Particle   Oil                                         Composition of vinyl monomer (b)                                                                     diameter                                                                           Penetrating                                                                         absorption                                  MMA ST BA MAc                                                                              AAc                                                                              AM DVB [μ]                                                                             pore  (%)                                __________________________________________________________________________    Poly. Ex.                                                                     6            503                                                                              60 36       1   0.51 ◯                                                                       82                                 7        342 240   12    6      0.54 ◯                                                                       78                                 8        370 180                                                                              20 30           0.60 ◯                                                                       78                                 9        589          6  3  2   0.56 ◯                                                                       80                                 10       108 480   12           0.40 ◯                                                                       70                                 11       312    80 8            0.41 ◯                                                                       75                                 12       624    160                                                                              16           0.62 ◯                                                                       83                                 Comp. Poly. Ex.                                                               * 6      468    120                                                                              12           0.52 X     56                                 ** 7     360    120                                                                              120          --   --    --                                 8        438    12 12       30  0.44 X     50                                 *** 9    468    120                                                                              12           0.49 X     52                                 **** 10  468    120                                                                              12           0.48 X     51                                 11       39     10 1            0.35 X     51                                 12       1404   360                                                                              36           0.83 X     49                                 __________________________________________________________________________     * Polymer (B) is obtained by redox polymerization. Void is found in the       interior. No penetrating pore is found.                                       ** Polymer (C) coagualtes in the polymerization. Emulsion cannot be           formed.                                                                       *** Emulsion of vinyl monomer (b) is added over 6 hours (6 times of           Polymerization Example 1). Void is found in the interior. No penetrating      pore is found.                                                                **** Emulsion of vinyl monomer (b) is added over 20 minutes (1/3 times of     Polymerization Example 1).                                                    ***** Void is found in the interior. No penetrating pore is found.       

                                      TABLE 3                                     __________________________________________________________________________                                  Particle   Oil                                           Composition of vinyl monomer (c)                                                                   diameter                                                                           Penetrating                                                                         absorption                                    ST MMA i-BMA                                                                             AN MAc                                                                              DVB [μ]                                                                             pore  [%]                                  __________________________________________________________________________    Poly. Ex.                                                                     13          297     3         0.48 ◯                                                                       80                                   14       297           3      0.48 ◯                                                                       79                                   15       297              3   0.45 ◯                                                                       77                                   16       97     200 3         0.39 ◯                                                                       71                                   17       198        2         0.41 ◯                                                                       75                                   18       396        4         0.62 ◯                                                                       83                                   19                            0.35 ◯                                                                       67                                   Comp. Poly. Ex.                                                               ** 13    285           15     --   --    54                                   *** 14   285              15  0.42 X     60                                   **** 15  297        3         0.40 X     51                                   *** 16   4950       50        1.05 X     55                                   __________________________________________________________________________     * Polymer (B) is treated with alkaline material without addition of vinyl     monomer (c).                                                                  ** Coagualtion occurs in polymerization process. Emulsion cannot be           obtained.                                                                     *** Void is found in the interior. No penetrating pore is found.              **** Treatment with alkaline material is carried out at pH 6.5.          

[Examples of Resin Composition for Paper Coating] Examples 1

The performance of emulsions obtained in the above PolymerizationExamples and Comparative Polymerization Examples were evaluated asorganic pigments and organic fillers for use in paper coating field.

The formulation and evaluation procedures are illustrated below.

    ______________________________________                                                                    Part                                              ______________________________________                                        Kaolin clay UW-90 (Trade mark of a product from EMC                                                         90                                              Co.)                                                                          Pigment or filler             10                                              Aron T-40 (Trade mark of a product from Toagosei                                                             0.09                                           Chemical Ind.)                                                                MS-4600 (Trade mark of a product from Nippon Food                                                            3                                              Industrial Co.)                                                               Polylac 755 (Trade mark of a product from Mitsui Toatsu                                                     12                                              Chemicals Inc.)                                                               Solid content of coating fluid                                                                              62%                                             ______________________________________                                    

The coating fluid was prepared by adding a pigment dispersant Aron T-40(sodium polyacrylate) having a solid content of 40% to water,sufficiently dispersion kaolin clay UW-90 with a Kaules mixer andfurther mixing with one of the emulsion obtained in PolymerizationExamples and Comparative Polymerization Examples as an organic pigment.

For the purpose of comparison, titanium dioxide paste having a solidcontent of 62% (a product of Dainichi Seika Co.) was used as aninorganic pigment and precipitated calcium carbonate slurry TP-222HShaving a solid content of 60% (a product of Okutama Industrial Co.) wasused as an inorganic filler. Phosphated starch MS-4600 as a binder andPolylac 755 having an SBR latex solid content of 50% were added asbinders to obtain coating fluids.

Using an applicator, each of the above obtained coating fluids wasapplied to wood free paper so as to give a dry pickup of 14 to 15 g/m²and then dried at 120° C. for 20 seconds. Thereafter, under suchconditions as a roll temperature of 60° C., a linear pressure of 70kg/cm² and a speed of 10 m/min, the applied paper was passed twicethrough calender rolls to obtain a coated paper, and its performance wasevaluated by the following methods.

Color viscosity:

Measured with a BM type viscometer at 60 r.p.m. by using a No. 4 rotor.

Gloss of coated paper:

Reflectance at an angle of 75° was measured in accordance with JISP-8142.

Printed gloss:

Using an RI printing tester, coated paper was printed with 0.4 cc of NewBright Indigo manufactured by Toyo Ink Co. After drying, reflectance atan angle of 75° was measured in accordance with JIS P-8142.

Brightness:

Measured with a Hunter color difference meter in accordance with JISP-8123.

Opacity:

Measured in accordance with JIS P-8138.

Dry pick:

Tested with an RI printing tester. In the evaluation, ten points wereregarded as a full mark.

Wet pick:

Tested with an RI printing tester. In the evaluation, ten points wereregarded as a full mark.

Ink acceptability with water:

Using a Morton roll on an RI printing tester, coated paper was printedwith addition of water. Printed color density was evaluated by visualobservation. In the evaluation, five points were regarded as a fullmark.

Ink setting:

Using an RI printing tester, coated paper was solid printed with 0.4 ccof ink. The printed surface was immediately brought into contact withtest paper and tested again with the RI printing tester. The amount ofink transferred to the test paper was measured with a Macbethdensitometer. A lower value indicates a better results.

Gas permeability:

Measured with a Ohken model gas permeability tester. A lower valueindicates a better result.

Results are illustrated in Table 4.

Examples 2-19

The particles prepared in Polymerization Examples 2-19 were evaluated bythe same procedures as described in Example 1. Results are illustratedin Table 4.

Comparative Examples 1-15

The particles prepared in Comparative Polymerization Examples 1-16(Comparative Polymerization Examples 4, 7 and 13, exclusive) wereevaluated by the same procedures as described in Example 1. The casewhere titanium dioxide or calcium carbonate was used singly (ComparativeExamples 14 and 15) was also evaluated.

Results are summarized in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                         Color                                                                              Gloss of               RI       Gas per-                                 viscosity                                                                          white                                                                              Printed                                                                           Bright-                                                                           Opac-                                                                             Dry                                                                              Wet                                                                              coloring                                                                           Ink meability           No.        Pigment or filler                                                                       (cps)                                                                              paper                                                                              gloss                                                                             ness                                                                              ity pick                                                                             pick                                                                             value                                                                              setting                                                                           (second)            __________________________________________________________________________    Example    Poly. Ex.                                                           1          1        1701 79.1 94.1                                                                              81.4                                                                              96.6                                                                              9  9  5    0.27                                                                              2550                 2          2        1684 78.5 94.0                                                                              80.8                                                                              96.4                                                                              9  9  5    0.27                                                                              2510                 3          3        1712 78.3 94.3                                                                              81.1                                                                              96.4                                                                              9  9  4    0.30                                                                              2860                 4          4        1687 79.2 93.8                                                                              80.8                                                                              96.3                                                                              9  9  5    0.28                                                                              2570                 5          5        1731 79.5 93.7                                                                              80.5                                                                              96.2                                                                              9  9  4    0.30                                                                              2790                 6          6        1710 79.9 93.6                                                                              81.3                                                                              96.3                                                                              9  9  4    0.30                                                                              2530                 7          7        1709 78.6 94.1                                                                              80.7                                                                              96.1                                                                              9  9  4    0.30                                                                              2520                 8          8        1731 78.4 89.8                                                                              81.1                                                                              96.3                                                                              9  9  4    0.30                                                                              2520                 9          9        1684 78.4 94.3                                                                              80.9                                                                              96.2                                                                              9  9  4    0.29                                                                              2640                10         10        1780 77.1 89.2                                                                              80.0                                                                              95.7                                                                              8  9  4    0.30                                                                              2860                11         11        1703 79.2 93.6                                                                              81.1                                                                              96.5                                                                              8  9  4    0.30                                                                              2930                12         12        1710 78.6 93.8                                                                              81.0                                                                              96.6                                                                              9  9  5    0.27                                                                              2530                13         13        1733 78.3 93.8                                                                              81.2                                                                              96.4                                                                              9  9  4    0.29                                                                              2540                14         14        1584 77.3 92.6                                                                              80.6                                                                              95.5                                                                              9  9  5    0.29                                                                              2730                15         15        1612 77.8 93.2                                                                              80.5                                                                              95.8                                                                              9  9  4    0.30                                                                              2690                16         16        1750 77.0 90.2                                                                              80.0                                                                              95.1                                                                              8  9  4    0.30                                                                              2960                17         17        1629 78.7 93.1                                                                              80.4                                                                              95.8                                                                              9  9  4    0.29                                                                              2980                18         18        1817 78.2 94.0                                                                              80.8                                                                              96.3                                                                              9  9  5    0.27                                                                              2500                19         19        1837 78.1 91.1                                                                              80.2                                                                              95.2                                                                              8  9  4    0.30                                                                              2990                Comparative Example                                                                      Comp. Poly. Ex.                                                     1          1        1695 75.9 88.3                                                                              78.7                                                                              94.2                                                                              8  8  2    0.33                                                                              3750                 2          2        1814 74.0 87.9                                                                              78.2                                                                              93.8                                                                              6  7  3    0.31                                                                              3190                 3          3        1792 76.4 88.6                                                                              78.4                                                                              95.8                                                                              7  8  3    0.32                                                                              3370                 4          5        1816 76.8 89.1                                                                              78.8                                                                              93.6                                                                              8  8  3    0.32                                                                              3320                 5          6        1831 76.3 88.1                                                                              78.9                                                                              95.1                                                                              7  8  3    0.32                                                                              3290                 6          8        1793 75.8 88.5                                                                              78.7                                                                              94.2                                                                              8  9  3    0.32                                                                              3310                 7          9        1977 76.8 89.0                                                                              78.8                                                                              94.0                                                                              7  6  3    0.32                                                                              3280                 8         10        1734 75.6 88.4                                                                              78.7                                                                              94.1                                                                              7  7  3    0.32                                                                              3290                 9         11        1856 74.3 88.1                                                                              78.6                                                                              94.3                                                                              7  6  2    0.32                                                                              3490                10         12        1736 76.5 88.4                                                                              78.4                                                                              93.8                                                                              8  8  3    0.31                                                                              3200                11         14        1678 77.8 90.2                                                                              80.0                                                                              94.8                                                                              7  8  3    0.32                                                                              3320                12         15        1755 75.7 89.6                                                                              79.3                                                                              94.9                                                                              7  8  3    0.32                                                                              3360                13         16        1764 76.8 88.7                                                                              78.6                                                                              94.5                                                                              7  9  3    0.31                                                                              3220                14         Titanium dioxide                                                                        1821 71.2 88.6                                                                              81.7                                                                              97.1                                                                              8  9  2    0.33                                                                              3800                15         Calcium carbonate                                                                       1229 69.7 88.4                                                                              77.4                                                                              93.7                                                                              8  9  3    0.30                                                                              3500                __________________________________________________________________________

[Examples of Resin Composition for Paint] Example 20

Paint formulations were prepared by using the particles obtained in theabove Polymerization Examples as organic pigments in place of a part ofrutile type titanium dioxide.

As a paint vehicle, an acrylic emulsion having a resin content of 45%,Trade Mark; Almatex E-208, was used. The formulations used for preparingthese paints are illustrated in Table 5.

                  TABLE 5                                                         ______________________________________                                        Water                      45.0   parts                                       Aqueous Tamol solution (Trade Mark of Rohm &                                                             12.2   parts                                       Haas Co.                                                                      Ethylene glycol            40.0   parts                                       2-amino-2-methyl propanol  3.0    parts                                       Nopco DF-122NS (Trade Mark of Sun Nopco Co.)                                                             0.8    parts                                       Rutile type titanium dioxide                                                                             164.5  parts                                       Emulsion prepared to 40% content                                                                         102.8  parts                                       Almatex E-208 (Trade Mark of Mitsui Toatsu                                                               676.0  parts                                       Chemicals Inc.)                                                               Butyl cellosolve/Taxanol (1/2) solvent mixture                                                           40.0   parts                                       Hydroxymethyl cellulose/propylene glycol (1/40)                                                          12.4   parts                                       mixture                                                                       Solid content in coating fluid                                                                           46.9%                                              PWC (wt % pigment in solid)                                                                              40.0%                                              Viscosity of paint         70-80 KU                                           ______________________________________                                    

Paints were prepared by charging water, Tamol 731, ethylene glycol,2-amino-2-methylpropanol, Nopco DF-122NS and rutile type titaniumdioxide into a pigment grinding mill and thoroughly dispersing theseingredients. Successively, one of the emulsion obtained in Examples andComparative Examples, Almatex E-208, butyl cellosolve/Texanol andhydroxyethyl cellulose/propylene glycol were added with stirring.Viscosity of the paints was adjusted to 70 to 80 KU by using a Stomerviscometer.

The paints thus prepared were applied to slates so as to give a dry filmthickness of about 40 μm, and dried at room temperature for a week.Then, the performance of the test specimen thus obtained was evaluatedby the following methods.

Gloss:

Measured at an angle of 60° with a glossmeter manufactured by SugaTesting Machine Co.

Hiding Power:

Measured in accordance with JIS K-5663, using an applicator, a paint tobe tested was applied to a sheet of hiding power test paper manufacturedby Japan Test Panel Industrial Co. so as to give a dry film thickness of75 μm, and dried at room temperature for a week. Thereafter, hidingpower was calculated from a 45°/0° reflectance ratio.

Water resistance:

The test specimen was submerged in water for 24 hours at roomtemperature. Thereafter appearance of the painted film was visuallyobserved.

Absence of disorder such as blister and whitening was judged ◯.

Alkali resistance:

The test specimen was submerged in a 2% aqueous sodium hydroxidesolution for 24 hours at room temperature. Thereafter appearance of thepainted film was visually observed.

Absence of disorder such as blister and whitening was judged ◯.

Weather resistance:

The specimen was irradiated in a weater-o-meter for 500 hours.Thereafter appearance of the painted film was visually observed.

Absence of disorder such as blister, whitening and decrease in gloss wasjudged ◯.

Washability:

The specimen was tested in accordance with JIS K-5663.

No peel off of the painted film after washing more than 2000 times wasjudged ◯.

No peel off of the painted film after washing from 1000 to 2000 timeswas judged Δ.

Adherence:

The painted film was given a crosscut with a cutter-knife. A cellophanetape was adhered to the crosscut portion of the painted film and thenpeeled off.

No stripping of the painted film at the crosscut was judged ◯.

Some stripping of the painted film at the crosscut was judged Δ.

Results of evaluation is illustrated in Table 6.

Examples 21-38

The particles prepared in Polymerization Examples 2-19 were evaluated bythe same procedures as described in Example 20. Results are illustratedin Table 6.

Comparative Examples 16-29

The particles prepared in Comparative Polymerization Examples 1-16(Comparative Polymerization Examples 4, 7 and 13, exclusive) wereevaluated by the same procedures as described in Example 20. The case ofusing titanium dioxide singly was evaluated in Comparative Example 29.

Results are illustrated in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                                      Hiding                                                          TiO.sub.2 /emuslion                                                                         power                                                                              Water                                                                              Alkali                                                                             Weather                                                                            Wash-                   No.        Emulsion particle                                                                      particle (w/w)                                                                         Gloss                                                                              (%)  resistance                                                                         resistance                                                                         resistance                                                                         ability                                                                            Pick               __________________________________________________________________________    Example    Poly. Ex.                                                          20          1       80/20    88   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      21          2       "        88   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      22          3       "        87   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      23          4       "        88   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      24          5       "        87   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      25          6       "        88   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      26          7       "        89   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      27          8       "        87   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      28          9       "        88   96   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      29         10       "        86   95   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      30         11       "        88   97   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      31         12       "        89   96   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      32         13       "        87   98   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      33         14       "        87   95   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      34         15       "        88   94   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      35         16       "        86   94   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      36         17       "        86   93   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      37         18       "        89   95   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      38         19       "        87   94   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      Comparative Example                                                                      Comp. Poly. Ex.                                                    16          1       "        81   88   X    X    ◯                                                                      ◯                                                                      ◯      17          2       "        80   88   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      18          3       "        81   90   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      19          5       "        82   91   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      20          6       "        83   90   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      21          8       "        80   88   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      22          9       "        82   90   X    X    ◯                                                                      X    ◯      23         10       "        80   88   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      24         11       "        82   89   X    X    X    ◯                                                                      ◯      25         12       "        81   91   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      26         14       "        83   91   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      27         15       "        81   90   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      28         16       "        80   89   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      29         --       100/0    78   99   ◯                                                                      ◯                                                                      ◯                                                                      ◯                                                                      ◯      __________________________________________________________________________

[Examples for Heat-sensitive Recording Materials]

Paper was used as a substrate and the multi-shell emulsion particle ofthe invention was used in the intermediate layer.

Examples 39-57 (1) Preparation of under coating compositions

Using the emulsion particles prepared in Polymerization Examples 1 - 19.A lend composed of 80 parts of the emulsion particle and 20 parts of abinder was thoroughly mixed to prepare an undercoating composition ofthe heat-sensitive recording material. Polyvinyl alcohol K-117 (Trademark of Kuraray) was used as a binder.

(2) Preparation of compositions for heat-sensitive recording layer

Using a sand mill, fluid A (a color forming dispersion) and fluid B (adeveloper dispersion) were separately prepared on the basis of thefollowing formulations.

    ______________________________________                                        Ingredient                 Part                                               ______________________________________                                        (Fluid A)                                                                     3-Dimethylamino-6-methyl-7-anilinofluoran                                                                20                                                 20% Aqueous hydroxyethyl cellulose solution                                                               5                                                 Water                      75                                                 (Fluid B)                                                                     Bisphenol A                20                                                 20% Aqueous hydroxyethyl cellulose solution                                                               5                                                 Microcrystalline wax, Petrolite R-50 (Trade Mark of                                                       5                                                 Halico Co.)                                                                   Water                      70                                                 ______________________________________                                    

After fluids A and B were thoroughly dispersed in a sand mill, 15 partsby weight of fluid A, 40 parts by weight of fluid B, 20 parts by weightof calcium carbonate, and 25 parts by weight of a 20% aqueous solutionof Polyvinyl Alcohol K-117 (manufactured by Kuraray) were mixed andstirred vigorously to obtain a heat-sensitive recording layercomposition.

Using a bar coater, each of the aforesaid undercoating composition wasapplied to commercially available wood free paper (having an arealweight of about 50 g/m²) so as to give a dry pickup of 15 g/m² and thendried. Subsequently, using a bar coater, the aforesaid thermal recordinglayer composition was applied thereto so as to give a dry pickup ofabout 15 g/m² and then dried to obtain a heat-sensitive recording paper.

Brightness of the paper was measured with a Hunter color differencemeter in accordance with JIS P-8123.

Color density was tested by developing color under the followingconditions with a heat-sensitive paper printing apparatus TH-PMD (TradeMark of Okura Electric Co.). Density of developed color was measuredwith a Macbeth densitometer.

Applied voltage 24 V. Pulse width 1.74 ms.

Applied energy 0.34 mJ/dot.

Further, sticking and foreign matter adhesion to the head were tested byprinting under the following conditions.

Applied voltage 27 V. Pulse width 3.0 ms.

Applied energy 0.73 mJ/dot.

As a result of the sticking and adhesion test, printability wasclassified into ⊚, ◯, Δ, X, and XX. Results are illustrated in Table 7.

Comparative Examples 30-42

Emulsion particles prepared in Comparative Polymerization Examples 1-16(Comparative Polymerization Examples 4, 7 and 13, exclusive) wereevaluated by the same procedures as described in Examples 39-57.

Results are illustrated in Table 7.

                  TABLE 7                                                         ______________________________________                                                            Print    Print-                                           No.      Particle   density  ability                                                                              Brightness                                ______________________________________                                        Example  Poly. Ex.                                                            39        1         1.39     ⊚                                                                     80.9                                      40        2         1.34     ◯                                                                        80.3                                      41        3         1.33     ⊚                                                                     80.4                                      42        4         1.30     ◯                                                                        80.1                                      43        5         1.31     ⊚                                                                     80.7                                      44        6         1.33     ⊚                                                                     80.6                                      45        7         1.36     ⊚                                                                     80.0                                      46        8         1.32     ◯                                                                        80.4                                      47        9         1.30     ⊚                                                                     80.7                                      48       10         1.35     ◯                                                                        80.3                                      49       11         1.39     ⊚                                                                     80.7                                      50       12         1.31     ⊚                                                                     80.8                                      51       13         1.31     ◯                                                                        80.6                                      52       14         1.30     ⊚                                                                     80.1                                      53       15         1.38     ⊚                                                                     80.0                                      54       16         1.34     ◯                                                                        80.0                                      55       17         1.37     ⊚                                                                     80.2                                      56       18         1.36     ⊚                                                                     80.8                                      57       19         1.30     ◯                                                                        80.7                                      Comparative                                                                            Comp. Poly.                                                          Example  Ex.                                                                  30        1         1.09     Δ                                                                              78.4                                      31        2         1.00     X      78.0                                      32        3         1.02     Δ                                                                              78.8                                      33        5         1.05     Δ                                                                              77.5                                      34        6         1.02     X      78.6                                      35        8         1.07     X      78.9                                      36        9         1.00     Δ                                                                              78.2                                      37       10         1.08     Δ                                                                              78.2                                      38       11         1.09     Δ                                                                              78.5                                      39       12         1.06     Δ                                                                              78.1                                      40       14         1.04     X      77.8                                      41       15         1.01     XX     78.6                                      42       16         1.10     Δ                                                                              78.0                                      ______________________________________                                    

What is claimed is:
 1. A multi-shell emulsion particle prepared byemulsion polymerization of one or more vinyl monomers, comprising a drystate structure having one or more penetrating pore(s) connecting thesurface layer of the particle with the interior of the particle andhaving a particle diameter of from 0.1 to 5.0 μm.
 2. The emulsionparticle of claim 1 wherein the particle has a void in the interior ofthe particle in a dry state and one or more penetrating pores from theparticle surface to the interior void.
 3. The emulsion particle of claim1 wherein the diameter of the particle is in the range of from 0.1 to1.2μ.
 4. The emulsion particle of claim 1, wherein the one or more vinylmonomers are selected from the group consisting of methyl (meth)acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, styrene,α-methylstyrene, vinyltoluene, (meth) acrylonitrile, vinyl chloride,vinylidene chloride, butadiene and mixtures thereof.
 5. The emulsionparticle of claim 1, wherein the one or more vinyl monomers arepolymerized with a further functional monomer.
 6. The emulsion particleof claim 5, wherein the functional monomer is selected from the groupconsisting of unsaturated sulfonic acid salts, dimethylaminoethylmethacrylate, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate,(meth)acrylamide, N-methylol(meth)acrylamide and mixtures thereof. 7.The emulsion particle of claim 1, wherein the one or more vinyl monomersare polymerized with a further crosslinkable monomer.
 8. The emulsionparticle of claim 7, wherein the crosslinkable monomer is selected fromthe group consisting of divinylbenzene, ethylene glycoldi(meth)acrylate, trimethylolpropane tri(meth) acrylate and mixturesthereof.
 9. The emulsion particle of claim 7, wherein the crosslinkablemonomer is present in an amount of 0.1 to 8% by weight of the polymer.10. The emulsion particle of claim 1, which comprises an interior of apolymer (A) formed by emulsion polymerization of one or more vinylmonomers and an exterior of a polymer (B) formed by polymerization ofone or more vinyl monomers.
 11. The emulsion particle of claim 10, whichfurther comprises an exterior of a polymer (C) formed by emulsionpolymerization of one or more vinyl monomers.
 12. The emulsion particleof claim 11, wherein the amount of polymer (C) is 1 to 20 times byweight of the total weight of polymer (A) and polymer (B).
 13. Theemulsion particle of claim 10, wherein the amount of polymer (B) is 1 to10 times by weight of the weight of polymer (A).